1. Field of the Invention
The present invention relates to a high frequency switch device, and particularly to a high frequency switch device employed in a wireless communication apparatus, a satellite communication apparatus and a satellite broadcasting apparatus.
2. Description of the related Art
With a sudden proliferation of wireless communication apparatuses such as a cellular phone, a wireless LAN, etc. and more functionality or the like of information devices and systems due to a multichannel configuration of satellite broadcasting, there has recently been a sharp increase in demand for a high frequency switch employed in RF transmit-receive units of these devices and systems.
The high frequency switch is used for switching between transmission and reception and switching between call modes in the case of a cellular phone and used for selection of signals from satellites of plural models in the case of a satellite dish. The high frequency switch is ranked an indispensable electronic device which supports an information and communication society.
The high frequency switch needs to have characteristics that (1) power consumption thereof is low, (2) its insertion loss is small and a leak of input power to other paths is low at its OFF, i.e., high isolation is enabled and high performance can be realized, (3) multifunctioning and a size reduction thereof are easy, (4) its low cost is realized, for example. As a high frequency switch that meets these, a high frequency switch configured of a microwave integrated circuit (MMIC) with GaAs FETs as bases is being put to use with growing frequency.
A GaAs MMIC switch using these FETs has been widely used for switching between signal paths and selection of a specific signal in a high frequency device used in a band of approximately 0.8 to 10 GHz. A high frequency switch used in conjunction with multifunctioning of a high frequency device and an increase in capacity for transmitted/received information and its diversification or the like has also been moved toward high functioning as in the case of the conventional SPDT (single pole double throw, 1×2) to SP3T (single pole 3 throw, 1×3) and SP4T (single pole 4 throw, 1×4) and to a matrix switch such as a 4×2 switch (4×2 Switch Matrix).
As a well-known example of the conventional high frequency switch, there is known a 4×2SW using FETs, for example. The 4×2SW is configured by integrating eight switch elements on a GaAs substrate.
In order to allow one switch element to include four FETs, 32 FETs are used in total. Since two-systematic lines for control signals are respectively needed to ON/OFF control the respective switch elements, sixteen-systematic lines for control signals are used over the whole high frequency switch.
In general, an N×M switch (N×M Switch Matrix) needs (2×N×M) control terminals, and hence the number of terminals materially increases with high functioning of a high frequency switch. In the present 4×2 switch, a decoder IC as well as a switch circuit is also brought into integration to suppress an increase in the number of the terminals and perform switching between signals on the 16-systematic control signal lines (see, for example, Hittite v04.0701: Catalog of HMC276QS24 produced by Hittite Microwave Corporation).
As another well-known example of other high frequency switch, there has been proposed a configuration wherein a switch circuit using distributed constant type FETs is used in each SPDT, so that a less reduced passage loss can be obtained upon switch ON and high isolation can be expected upon switch OFF (see, for example, Japanese Patent Laid-Open No. 2002-33602, the paragraph numbers [0013] and [0014] and FIG. 1).
As yet another well-known example of other high frequency switch, there has been disclosed a high frequency switch which includes a plurality of tristate switches, which are connected in tournament form by strip lines and wherein the lengths of the strip lines from branch points of the lines connected to the respective switches to their corresponding switches are adjusted in such a manner that the real part of impedance at the time that the switches each held in an off state are seen from the branch points, reaches the maximum and the imaginary part thereof is brought to 0, and the lengths from the basic branch points of the lines connected to the respective branch points to the respective corresponding branch points are respectively adjusted to an integral multiple of a ½ wavelength (see, for example, Japanese Patent Laid-Open No. 2000-261218, the paragraph number [0006] and FIG. 1).
As a still further well-known example of other high frequency switch, there has been disclosed one in which when four or more receiving antennas are switched in a holographic radar, a single pole double throw (SPDT) output type or single pole 3 throw (SP3T) output type unit switch, e.g., a plane circuit type high frequency switch such as MMIC, HIC or the like is used, and such unit switches are utilized in combination in tournament form for the purpose of realization of multiswitching (see, for example, Japanese Patent Laid-Open No. 2000-155171, the paragraph number [0005] and FIG. 5).
The conventional high frequency switch must be provided with a control decoder IC circuit aside from a switch unit to reduce the control terminals in number. Thus, a chip area increased and a reduction in cost could not be achieved sufficiently. Since a logic circuit of a decoder IC unit is fine and complex as compared with the switch unit, process yields are reduced and hence a reduction in cost could not be achieved sufficiently due to the reduction in the yield.
On the other hand, when no decoder circuit is brought into integration, the N×M switch needs (2×N×M) control terminals and needs to control (2×N×M) lines for control signals independently. It is thus necessary to provide (2×N×M) control pins. Therefore, the N×M switch resulted in upsizing of a chip and a package and an increase in cost.
Further, when a plurality of switch elements are connected in tournament form to reduce the number of the control pins, the setting of impedance of each connecting wiring becomes complex to realize high isolation of the high frequency switch, so an increase in complexity of a circuit configuration cannot be avoided. Such a high frequency circuit that a circuit configuration on a chip is greatly affected by its electric characteristic, unavoidably resulted in a reduction in the degree of freedom of circuit design.
As described above, the conventional high frequency switch is accompanied by the problems that when the decoder circuit is added thereto, its size reduction and low cost cannot be achieved, whereas when no decoder circuit is added, the number of the control pins increases, thus resulting in upsizing of the chip and package and the increase in cost, and when an attempt is made to reduce the number of the control pins and achieve high isolation, the setting of impedance in the circuit becomes complex and the degree of freedom of design is degraded, for example.